This invention relates to a metallic vapor condenser for use in recovering, in the form of molten metal, a metal which has a medium boiling point between a high and a low boiling points and which may be, for example, zinc (Zn), cadmium (Cd), lead (Pb), or the like.
In general, a metal, such as zinc, cadmium, lead, is used in a dry battery and the like in large quantities. As well known, such a metal has a medium boiling point between 600.degree. C. and 2000.degree. C. and may be referred to as a medium boiling point metal. Heretofore, it is a recent trend that the metal is recovered to recycle or reuse the metal. For this purpose, a method is adopted such that vapor of the medium boiling point metal is quickly cooled or quenched to be recovered as molten metal. More particularly, the medium boiling point metal is once reduced and vaporized to be thereafter absorbed and condensed in a metal bath formed by the same metal by the use of a pyro-metallurgical refining technique. As a result, the metal is recovered in the form of molten metal.
Herein, it is to be noted that vapor of the medium boiling point metal tends to be easily reoxidized even in a high reducing atmosphere. In order to avoid such reoxidization of the molten metal, a shock chilling method has been practically enforced and has been classified into first and second methods as mentioned hereinunder.
According to the first method, the vapor of the medium boiling point metal is introduced into a condenser together with a reducing gas of, for example, CO with the vapor kept at a partial pressure and a temperature at which no oxidation of such metal vapor takes place. The vapor is thereafter brought into contact with a metal bath kept at a temperature which is slightly higher than a freezing point of the metal.
The metal vapor is introduced into a metal bath in such a method wherein the metal vapor is dispersed into the liquid metal bath by means of a submerged nozzle or an opening to form vapor bubbles in the bath (bubbler type).
In the second method, a condenser is used which comprises a splash chamber, a liquation sump, and a casting bath. Specifically, a metal bath is mechanically agitated within the splash chamber to cause splashes of metal liquid droplets to occur. In this situation, metallic vapor of metal of the medium boiling point is captured in the splash chamber which is being quickly brought into contact with the liquid metal. Consequently, the metallic vapor is condensed into the metal bath in the form of molten metal. Subsequently, the molten metal is cooled and is fed to the skimming sump to remove dross and dust which may be called impurities. The molten metal is further introduced into the liquation sump so as to separate impurities, such as a hard metal, which is an iron alloy. After removal of the dross and dust, the molten metal is reserved in the casting bath.
Inasmuch as the molten metal is finally reserved in the casting bath in the second method, it often happens that the molten metal is solidified before it is taken out from the casting bath to be cast into an ingot in the case where the condenser is small in size and the heat loss thereof is relatively high.
More specifically, if the second method is used for processing used dry batteries and/or dust, a quantity of recovery of the medium boiling point metal may be comparatively as small as 60 kg/hour and a comparatively large amount of dross takes place. Under the circumstances, application of the second method to such processing results in an excessive increase of a thermal loss.